Hi @prakash360 ,

There are a couple of things here:
1. You do not want to run ALTER TABLE commands on DLT. The idea of DLT is that they are fully managed by the DLT pipeline. Try to modify the DLT pipeline itself. 

2. At least try liquid clustering, as this a new, recommended feature. However, the liquid clustering in DLT was added just 2 weeks ago.

3. In order to make it work use preview 15.2 runtime and set channel of your DLT pipeline to preview: